For example, an inline-four-cylinder engine is configured to support pistons of four cylinders per crankshaft. In the engine of such a configuration, there are some which adopt a flat crankshaft (see Examined Japanese Patent Publication No. HEI 7-26546, for example).
The flat crankshaft is referred to as such because the phase angles of crank pins of the crankshaft (that is, crank phase angles) are arranged at 0 or 180 degrees. For example, No. 1 and No. 4 cylinders are in the same crank phase angle, and with respect to the crank phase angles of these cylinders, the crank phase angles of No. 2 and No. 3 cylinders are configured to be apart from the crank phase angles of No. 1 and No. 4 cylinders by 180 degrees.
Generally, in an engine which adopts such a flat crankshaft, a combustion control called “equally-intervalled combustion” may be carried out. The equally-intervalled combustion for the flat crankshaft is such that combustions of cylinders are sequentially carried out one by one as the crankshaft rotates every 180 degrees. For example, a combustion of No. 1 cylinder (#1) is carried out when the crank phase angle is 0 degrees, a combustion of No. 2 cylinder (#2) is carried out when the crank phase angle is 180 degrees, a combustion of No. 4 cylinder (#4) is carried out when the crank phase angle is 360 degrees, and a combustion of No. 3 cylinder (#3) is carried out when the crank phase angle is 540 degrees, so that a predetermined rhythm (feel of an engine beat) is produced.
However, the feel of the engine beat of equally-intervalled combustion is monotonous to the passenger. The feel of the engine beat is important because it dictates a ride quality and, thus, a development of an engine with a more comfortable feel of the engine beat has been always demanded.